U N I V E R S I T Y O F C O P E N H A G E N F A C U L T Y O F H E A L T H A N D M E D I C A L S C I E N C E S
D E P A R T M E N T O F V E T E R I N A R Y A N D A N I M A L S C I E N C E S
S E C T I O N O F A N I M A L G E N E T I C S , B I O I N F O R M A T I C S A N D B R E E D I N G
Veterinary Master’s Thesis
Lena Rahbek, wvc118
“Lanced” canines in the Shetland sheepdog,
heredity and breeding recommendations
Academic advisor: Professor Merete Fredholm
DVM, Ph.D., Dr.Vet.Sci.
Submitted on: 6 th of July 2018
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Name of department: Department of Veterinary and Animal Sciences, Section of Animal Genetics, Bioinformatics and Breeding
Author: Lena Rahbek Title and subtitle: “Lanced” canines in the Shetland sheepdog, heredity and breeding
recommendations Topic description: The aim of this study was to investigate whether “lanced” canines
is a hereditary condition in the Shetland sheepdog and to provide further elucidation of the condition itself together with health concerns and treatment options. Furthermore, to propose a breeding recommendation for the Shetland sheepdog regarding “lanced” canines.
Academic advisor: Professor Merete Fredholm
DVM, Ph.D., Dr.Vet.Sci. Submitted on: 6th of July 2018 Grade: Front page pictures: Left: Anonymous picture of one of the dogs participating in this
study. Right: Shetland sheepdog, photo credit to Kirsten Klitsgaard.
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Preface
This master’s thesis was conducted from February to July 2018 at Copenhagen University,
Faculty of Health and Medical Sciences, Department of Veterinary and Animal Sciences,
Section of Animal Genetics, Bioinformatics and Breeding in collaboration with the Danish
Shetland Sheepdog Club and the Danish Kennel Club.
The aim of this study was to find out if “lanced” canines in the Shetland sheepdog is a hereditary
condition and to propose some breeding recommendations in this regard. Furthermore, it was
also desirable to get an idea about the possible heritability and mode of inheritance.
The study was proposed by the Danish Shetland Sheepdog Club as a response to requests from
multiple breeders and Shetland sheepdog owners wishing to shed some light on the issue in the
breed. The club had also noticed that the problem seemed to be more widespread in certain lines.
They did not feel that they could take up the investigation themselves since some breeders might
not wish for their club to know that they have an issue in their kennel. Therefore, they wanted an
“outsider” to conduct the investigation and to make all information anonymous to encourage as
many breeders and dog owners as possible to submit data from their dogs to the study.
The process turned out to be more problematic than first expected since it was difficult to get
data about dogs with this condition and a lot of time was spend trying to get more dogs included
in the study. Furthermore, it was very difficult to find relevant articles about the genetics of tooth
disorders in dogs.
A literature search was performed in order to gather information about tooth development, a
known tooth disorder, its genetic setup and treatment.
Tolstrup, 6th of july 2018
___________________________
Lena Rahbek
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Acknowledgments
I am very grateful to my academic advisor Professor Merete Fredholm for her guidance and help
through the entire process.
I would also like to thank the Danish Shetland Sheepdog Club, especially their health committee
for showing interest in the subject and starting up initial data collection. A special thanks to
health committee member Tine Wiberg Rasmussen for being my contact person in the Danish
Shetland sheepdog club, helping me with further data collection and answering any question I
had during the process of writing this thesis.
Furthermore, a special thanks to veterinary specialist Jens Ruhnau from AniCura
TandDyreklinikken for giving me a more practical insight into the clinical aspect of odontology
and lanced canines and for sharing some of his knowledge and expertise about the subject.
Thanks to the Danish Kennel Club for helping me with further data collection by contacting
selected dog owners.
A big thanks to all the breeders and dog owners that provided me with information and pictures
of their dogs to use in this study, without your willingness to let your dogs be part of this study I
could not have written this thesis.
Also, a big thank you to Dr. James Longden for constructive criticism and proofreading of the
thesis.
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Abstract
“Lanced canines” is a condition that predominantly affects Shetland sheepdogs, becoming
apparent when the permanent upper canines start to erupt. It is characterised by mesioversion of
tooth 104 and/or 204 and gives rise to several health issues/concerns among them retained
deciduous teeth, traumatic contact with the hard palate, tooth-on-tooth wear and increased risk of
periodontal disease. The treatment methods include surgical extraction, corrective regulation
with elastic bands and corrective surgery.
Tooth development is a complicated process that includes many stages and developmental
processes, all of which are regulated by genes. To date no specific genetic components of
“lanced” canines have been discovered however comparable diseases, such as Primary failure of
eruption (PFE), have known genetic associations, in this case a mutation is seen in the PTHR1
gene, demonstrating that tooth disorders can indeed be hereditary.
It was the aim of this study to find out if “lanced” canines in the Shetland sheepdog is a
hereditary condition and to propose some breeding recommendations in this regard. To do this,
35 dogs known to have “lanced” canines and 25 dogs described as unaffected were included in
this study. 4-generation pedigrees were studied and through Singles method 11 whole litters
were analysed. This analysis found that we could not reject a null-hypothesis about simple
recessive inheritance. However, there were no common ancestors shared between all the 35
affected dogs, which when compared to the results from Singles method would suggest that
“lanced” canines is a condition with a high heritability, most likely a threshold trait caused by
mutations in several genes. Breeding recommendations must take other diseases/conditions in
the Shetland sheepdog breed into consideration. It is therefore recommended to not use any
affected individuals in breeding, furthermore to not repeat any mating that has resulted in
affected offspring.
The next step should be to try and calculate the prevalence and heritability of the condition in the
Danish Shetland sheepdog population and to identify the gene(s) causing “lanced” canines in
order to develop a genetic test for the condition. For this, further studies would be required.
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Resumé
Lansetænder er en tilstand der hovedsageligt rammer Shetland sheepdogs. Tilstanden bliver først
synlig når hjørnetænderne i overmunden begynder at bryde igennem. Lansetænder er karakteriseret
ved mesioversion af tand 104 og/eller 204 og giver grobund for adskillige sundhedsproblemer og
bekymringer heriblandt tilbageholdte mælketænder, traumatisk kontakt med den hårde gane, tand-
mod-tand slid og øget risiko for peridontale sygdomme. Behandlingsmetoder inkluderer
tandekstraktion, korrigerende regulering med elastik samt korrigerende operation.
Tændernes udvikling er en kompliceret proces der indeholder mange forskellige stadier og
udviklingsprocesser, alt sammen genetisk reguleret. Den genetiske baggrund for lansetænder kendes
endnu ikke, men jeg har gennemgået en sammenlignelig sygdom, Primary failure of eruption (PFE)
som har en kendt genetisk årsag, en mutation i PTHR1 genet, hvilket demonstrerer at
tandsygdomme godt kan være arvelige.
Formålet med dette studie var at finde ud af om lansetænder er en arvelig tilstand og at komme med
nogen avlsanbefalinger. I mit studie indgik 35 hunde med lansetænder og 25 hunde beskrevet som
værende fri for lansetænder. 4-generations stamtavler blev studeret og ved hjælp af Singles metode
blev 11 hele kuld analyseret. Af denne analyse fremgik det at man ikke kan forkaste en nulhypotese
om simpel resesiv arvegang. Der var ingen fælles forfædre delt mellem alle de 35 hunde med
lansetænder og dette, sammenholdt med resultatet fra Singles metoden ledte til konklusionen at
lansetænder er en tilstand med høj heritabilitet, mest sandsynligt en tærskelegenskab forårsaget af
mutationer i adskillige gener. Avlsanbefalinger skal sammenholdes med andre sygdomme i shetland
sheepdog racen. Det anbefales at man ikke bruger afficerede hunde i avl, samt at man ikke gentager
en parring der tidligere har resulteret i afficerede afkom.
Næste skridt må være at finde frem til prævalensen samt heritabiliteten af lansetænder i den danske
shetland sheepdog population og at identificere det/de gen/gener samt mutation/er der forårsager
lansetænder således at man kan udvikle en genetisk test for lansetænder. For at gøre dette er
yderligere studier nødvendige.
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List of abbriviations
CRL – Crown-rump length
DEJ – Dentino-enamel junction
DKK – Dansk Kennel Klub (The Danish Kennel Club)
FCI – Fédération Cynologique Internationale (World Canine Organization)
LC – Lanced canines
PFE – Primary failure of eruption
PTH – Parathyroid hormone
PTHLH - Parathyroid hormone like hormone
PTHR1 - Parathyroid hormone receptor 1
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Table of contents
PREFACE ............................................................................................................................ 3
ACKNOWLEDGMENTS ...................................................................................................... 4
ABSTRACT ......................................................................................................................... 5
RESUMÉ ............................................................................................................................. 6
LIST OF ABBRIVIATIONS .................................................................................................. 7
TABLE OF CONTENTS ...................................................................................................... 8
1. INTRODUCTION ........................................................................................................... 10
1.1 “Lanced” Canine Teeth. Definition, problems and treatment .............................................................................. 10
1.1.1 Definition ............................................................................................................................................................ 10
1.1.2 Health concerns and problems ............................................................................................................................ 10
1.1.3 Treatment options ............................................................................................................................................... 11
1.2 Tooth development ................................................................................................................................................... 14
1.2.1 Stages .................................................................................................................................................................. 14
1.2.2 Development ....................................................................................................................................................... 15
1.2.6 Gene expression and tooth development ............................................................................................................. 16
1.3 Genetics, heredity and teeth ..................................................................................................................................... 17
2. PRIMARY FAILURE OF ERUPTION (PFE) – A LITERATURE REVIEW ..................... 18
2.1 Background ............................................................................................................................................................... 18
2.2 Clinical impact, health concerns and treatment..................................................................................................... 18
2.3 Inheritance ................................................................................................................................................................ 19
2.4 Molecular genetic analysis ....................................................................................................................................... 19
2.5 Conclusion ................................................................................................................................................................. 20
3. MATERIALS AND METHODS ...................................................................................... 21
3.1 Segregation analysis .................................................................................................................................................. 21
3.1.1 Data collection for segregation analysis.............................................................................................................. 21
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3.1.2 Singles method .................................................................................................................................................... 21
3.2 My data ...................................................................................................................................................................... 22
3.2.1 Data collection and potential issues .................................................................................................................... 22
4. RESULTS ...................................................................................................................... 24
4.1 Overview .................................................................................................................................................................... 24
4.2 Singles method .......................................................................................................................................................... 24
5. DISCUSSION ................................................................................................................ 26
5.1 Heredity and “lanced” canines ................................................................................................................................ 26
5.2 Breeding restrictions and recommendations in the shetland sheepdog ............................................................... 26
5.2.1 Restrictions ......................................................................................................................................................... 26
5.2.2 Recommendations ............................................................................................................................................... 27
5.3 “Lanced” canines and breeding ............................................................................................................................... 27
5.4 Genetic testing ........................................................................................................................................................... 28
5.4.1 Genetic testing in general .................................................................................................................................... 28
5.4.2 Why is finding a possible genetic test a good idea? ............................................................................................ 28
6. CONCLUSION ............................................................................................................... 30
6.1 My study .................................................................................................................................................................... 30
6.2 Breeding recommendations regarding “lanced” canines ...................................................................................... 30
7. PERSPECTIVES ........................................................................................................... 31
REFERENCES .................................................................................................................. 32
APPENDIX ........................................................................................................................ 34
Appendix A – Dog owner questionnaire ....................................................................................................................... 34
Appendix B – Initial data overview ............................................................................................................................... 35
Appendix C – Litter compositions litters A till K ........................................................................................................ 36
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1. Introduction
1.1 “Lanced” Canine Teeth. Definition, problems and
treatment
1.1.1 Definition
“Lanced” canine teeth is a mesioversion of tooth 104 and/or 204. It predominantly affects
Shetland Sheepdogs, but a few other breeds such as Italian greyhounds, miniature schnauzers,
fox terriers and some cats can also be affected by this condition (Legendre and Stepaniuk 2008).
The adult upper canine tooth is displaced forward, pointing towards the nose. The degree of
displacement varies a lot. Because of the displacement the upper canine tooth can then be located
in front of the lower canine instead of behind it as is normal. Where the normal upper canine
tooth is almost perpendicular in relation to the hard palate, a “lanced” canine Tooth is located
more parallel to the hard palate.
The deciduous teeth are positioned normally and therefore it does not become evident that the
dog has “lanced” canine teeth until the adult canines erupt.
Figure 1: Shetland sheepdog with normally Figure 2: Shetland sheepdog with “lanced” upper
placed upper left canine. (Anonymous picture) left canine. (Anonymous picture)
1.1.2 Health concerns and problems
The abnormal position of the canine tooth can result in several problems (Legendre and
Stepaniuk 2008) and can even prevent the mouth from closing completely. If the diastema
between the lanced tooth and the lateral incisor is too small it can also prevent the lower canine
(304 and 404) from growing into a normal position between those teeth. The lower canine is then
forced to deviate from its normal position either labially or lingually. This can cause painful
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traumatic contact with the hard palate, irregular contact with the lip and tooth-on tooth wear that
can result in concussive pulpitis and possible pulp necrosis. Furthermore, food and calculus can
accumulate between the lanced tooth and the adjacent incisor, which can increase the risk of
periodontal disease between these two teeth. When the permanent teeth grow out in an abnormal
position the normal pressure on the deciduous tooth can also be lacking resulting in retained
deciduous teeth.
1.1.3 Treatment options
Optimal treatment strategy is dependent on several factors including the age of the dog, the
severity of the disease, the dog’s general health status and owner compliance and economy (Jens
Ruhnau, personal communication, May 28, 2018). Sometimes the displacement of the canine
tooth is only cosmetic and therefore does not require any correction, however if correction is
required this can be achieved through surgical or non-surgical means:
• Surgical extraction
Surgical extraction of a maxillary tooth can be performed using a scalpel to sever the epithelial
attachment of the maxillary tooth (Tsugawa, Lommer, and Verstraete 2012). Making sure the
flap is of sufficient width to allow the suture line to rest over solid bone and not the vacated
alveolus. Hereafter the tooth is loosened with a periosteal elevator. An alveolectomy (removal of
alveolar bone surrounding the tooth) is performed and the tooth is then loosened even more using
a luxator. When the tooth is sufficiently mobile the extraction forceps can be used to deliver the
tooth. The flap is then sutured in place.
• Corrective regulation with elastic band (orthodontic movement)
There are different techniques to achieve this, one example as recommended by Legendre and
Stepaniuk (Legendre and Stepaniuk 2008) is as follows: Depending on the side of the lanced
canine either 108 together with 109 or 208 together with 209 are used as anchor teeth. A lingual
button is fixed to the mesiobuccal cusp of the maxillary first molar tooth using an orthodontic
bonding agent. Hereafter a maxillary central incisor bracket, with its base slightly bent to better
follow the contour of the mesial cusp of the maxillary fourth premolar tooth, is bonded in place.
Next a length of orthodontic bracket tie wire is twisted from the lingual button to the distal
prongs of the bracket. The twisted end is cut short and pushed in between the distal prongs in
such a way that there is no irritation to the patient. Finally an elastic chain is cut at 80 to 75% of
its resting length and stretched from the hook to the mesial two prongs of the bracket. The elastic
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chain is changed every 2-weeks until the desired position of the target tooth is attained. Then the
appliances are removed.
This method can be used on dogs of any age, but the older the dog, the longer it will take. For
example, it takes approximately 2-3 months to reposition the tooth in dogs 7-8 months of age but
4-5 months for dogs 1 year of age (Jens Ruhnau, personal communication, May 28, 2018).
Before the procedure both the tooth/teeth to be moved and the teeth serving as anchor teeth must
be radiographed to ensure that their root systems are mature and healthy enough to withstand
orthodontic treatment without undue damage (Legendre and Stepaniuk 2008).
Figure 3: Corrective regulation. On the left dog with a left lanced canine that has just had regulation appliances
put on. On the right the same dog after the end of corrective regulation, now with a tooth 204 that is no longer
“lanced” (Picture from AniCura TandDyreklinikken).
• Corrective surgery
A third, novel, method that has not yet been described in the litterature (Jens Ruhnau, personal
communication, May 28, 2018) is to move the tooth’s position by changing the way the root is
positioned, similar to the method described above. But with this method it is all done in just 1
surgery where force is applied in order to “break” the root so that when the root continues to
grow it will grow at a crooked angle. For this surgery to be effective it is necessary that the tooth
is still root-open, i.e. that the root is still developing and maturing. In practise this means that this
kind of surgery must be performed preferably around 6 months of age, but no older than 8
months, when the “lanced” canine has just started to erupt. Corrective surgery is therefore not an
option for dogs with a fully developed “lanced” canine. After that regulation will have to be
done by the methods described above instead. It is recommended that the dog return to the clinic
a few months after to check if the surgery was a success.
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Figure 4: Corrective surgery. Left picture shows a dog with a retained deciduous upper left canine and a “lanced”
canine about to erupt. Middle picture shows the same dog after having the retained deciduous tooth removed and
corrective surgery performed. Right picture shows the same dog 4 months later now with a normally placed left
upper canine.
• Methods comparison
As corrective surgery or corrective regulation can save the tooth these are generally considered
the methods of choice (Legendre and Stepaniuk 2008). However surgical tooth extraction is a
more readily available treatment compared to corrective regulation and corrective surgery since
these procedures require technical expertise by the veterinarian and more advanced equipment.
In addition, both tooth extraction and corrective surgery can be performed in only one visit to the
veterinary clinic, whereas regulation with the elastic chain requires multiple office visits together
with an almost daily oral hygiene routine for the dog undergoing treatment. This also makes
regulation using the elastic chain more expensive compared to the other two methods, at roughly
double the price (Jens Ruhnau, personal communication, May 28, 2018). Given that corrective
surgery is only applicable before the “lanced” canine has fully developed it is generally
considered optimal to perform corrective surgery in dogs up to 8 months old, after which
corrective regulation should be used (Jens Ruhnau, personal communication, May 28, 2018).
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1.2 Tooth development
The deciduous dentition develops during the embryonic and foetal stages of a dogs gestation
period, whereas the permanent dentition develops during the foetal and neonatal stages of
development (Tutt 2006). A dogs gestation period is approximately 61 days (Pretzer 2008) with
the embryonic stage lasting until day 35, then the foetal stage begins and last until birth. The
neonatal stage last from birth until approximately 3 weeks of age (Bartges et al. 2012).
During this time tooth development progresses through several stages termed initiation, bud, cap
and bell (Tutt 2006).
1.2.1 Stages
• Initiation stage (12-16 mm CRL ((Williams and Evans 1978) )
In order for the initiation to begin, interaction between different embryological tissue is
necessary. This interaction, also known as induction, occurs between mesenchymal tissue and
ectodermal tissue (Tutt 2006).
The oral epithelium is derived from ectoderm. The ectoderm is separated from the underlying
mesenchyme by the basement membrane. Firstly, a narrow band of thickened epithelium
(primary epithelial band) forms on the developing mandible and maxilla (Teaford, Ferguson, and
Meredith Smith 2000). These bands specify the areas of epithelium from which teeth are capable
of forming, later on giving rise to the dental lamina when it grows down into the mesenchyme
(Tutt 2006)
• Bud stage (27 mm CRL / 32 days (Williams and Evans 1978) )
The dental lamina that has now been formed proliferates into the mesenchyme where it forms
buds. It is from these buds that the teeth will develop later on. All teeth develop from ectoderm
and mesoderm (Tutt 2006).
• Cap stage (33 mm CRL / 35 days (Williams and Evans 1978) )
Parts of the tooth bud undergo differential growth which leads to a cap shape. During this stage
the shape of the tooth is determined by the process of morphogenesis. The enamel organ, which
is of ectodermal origin, develops during this stage deep within the tooth bud and will later on
produce enamel that will cover the surface of the crown. The dental papilla, giving rise to dentin
and pulp, is formed by mesenchymal tissue. The dental sac, from which the periodontium will
develop, is formed from the mesenchyme surrounding the enamel organ (Tutt 2006).
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• Bell stage (72 mm CRL / 42 days (Williams and Evans 1978) )
During this stage proliferation, morphogenesis and differentiation continues. The cells of the
enamel organ differentiate into four distinct layers: Inner enamel (dental) epithelium which
differentiate into first pre-ameloblasts and, later on, ameloblasts that produce enamel, stratum
intermedium that supports enamel production, stellate reticulum, that also supports enamel
production, and outer enamel (dental) epithelium that protects the enamel organ during
amelogenesis.
The dental papilla differentiates into two layers: The outermost layer that will differentiate into
odontoblasts and produce dentin. The inner layer develops into the tooth pulp.
The dental sac differentiates into its separate tissues (gingiva, alveolus, periodontal ligament and
cementum) at a later stage (Tutt 2006).
1.2.2 Development
Further development occurs when the odontoblasts start to produce pre-dentine and the basement
membrane starts to disintegrate. Upon contact with pre-dentin the pre-ameloblasts develops into
ameloblasts. The ameloblasts start amelogenesis where they secrete enamel matrix onto the
disintegrating basement membrane, thereby forming the dentino-enamel junction (DEJ). The
ameloblasts produce primary dentin until apexogenesis is complete, hereafter they produce
secondary dentin throughout the lifespan of the tooth (Tutt 2006).
Root development starts once the crown is fully formed and begins to erupt into the mouth. The
root is formed by the cervical loop, that is a portion of the original enamel organ. The cervical
loop grows down into the dental sac enclosing more of the dental papilla forming Hertwig’s root
sheath which determines the shape of the root / roots. Production of pre-dentine begins and the
root continues to develop until the apex is formed. When the basement membrane and Hertwig’s
root sheath disintegrates, thereby exposing undifferentiated cells from the dental sac to the root
dentine, these cells become cementoblasts. The cementoblasts secrete cementoid that undergoes
mineralisation into cementum.
During the development of the root and the crown, mesenchyme from the surrounding dental sac
starts to form the periodontal ligament and the alveolus. This ligament is designed to withstand
rotational force and other forces applied to the tooth to keep it within the alveolus.
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1.2.6 Gene expression and tooth development
• Initiation and tooth bud formation
As mentioned above the tooth development process starts with the formation of the primary
epithelial band and then tooth buds forming at specific places in the dental lamina. This process
is controlled, at least in part, by the Msx-1 and Msx-2 homeobox genes, which are both
expressed in epithelial and mesenchymal cells during tooth development (Teaford, Ferguson, and
Meredith Smith 2000). Early expressions domains of Msx-1 and Msx-2 prior to tooth bud
formation suggest a role for these genes in initiating the primary epithelial band a hypothesis that
was further supported by in vivo experiments in which targeted mutation of the Msx-1 gene
resulted in the development of all teeth being arrested in the early bud stage (Satokata and Maas
1994).
It has also been suggested that Msx-1 is required for a signalling pathway from bud mesenchyme
to dental epithelium in tooth histogenesis by regulating the expression of signalling molecules,
possibly Bmp-4 (Teaford, Ferguson, and Meredith Smith 2000).
Tooth development in Msx-1/Msx-2 double mutants is reported as being arrested earlier than the
tooth bud stage and initiation may not occur at all when both genes are absent.
• Tooth positioning and shape
The ‘odontogenic homeobox code’ is a molecular model for the patterning of the dentition, based
on the expression of several homeobox genes in neural crest-derived ectomesenchyme (Sharpe
1995). The expression of homeobox genes such as Dlx-1, Dlx-2, Msx-1 and Msx-2 are proposed
to specify the development of tooth germs into either molars or incisors. So different genes
regulate the formation of teeth at different positions. For example, Dlx-1/ -2 -/- embryos have
normal upper and lower incisors and lower molars, but do not develop any upper molars (Qiu et
al. 1997; Thomas et al. 1997). Further supporting the specificity of gene regulation between the
different teeth is the fact that null mutation of the activin-βA gene (activin is a growth factor-like
signalling molecule) in transgenic mice makes them develop no incisor teeth and no mandibular
molars, but the development of maxillary molars is always normal (Matzuk et al. 1995).
• Regulation of tooth shape
As described above the enamel knot is a part of the enamel organ that differentiates into different
cells that all play a role in the formation of the tooth shape and roots.
It has been proposed that Msx-2 expression provides a molecular link between tooth initiation
17
and shape (Mackenzie, Ferguson, and Sharpe 1992). Several more genes have been shown to be
restricted to enamel knot epithelial cells in the tooth bud, for example the expression of the genes
for the secreted factors Shh, Bmp-4, Bmp-7 and Fgf-4 are all localised in enamel knot cells. It
has also been proposed that the enamel knot acts as a signalling centre to direct secondary knot
formation which controls local epithelial cell proliferation rates (Vaahtokari et al. 1996).
1.3 Genetics, heredity and teeth
The genetic basis for “lanced” canines is currently un-known, with no specific inherited
component yet identified. Therefore, the following literature review will instead focus on another
tooth disease that is known to have an inherited genetic component in order to demonstrate how
tooth disorders can indeed be genetically inherited.
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2. Primary failure of eruption (PFE) – a literature review
As there are not any well-known tooth diseases that only effect the position of the tooth in the
same way as occurs with “lanced” canines primary failure of eruption (PFE) will instead be used
as an example of a comparable disease effecting the teeth.
2.1 Background
PFE is defined as incomplete tooth eruption despite the presence of a clear eruption pathway
where the alveolar bone above the crown has been reabsorbed (Hanisch et al. 2018; Stellzig-
Eisenhauer et al. 2010). It involves the partial or complete non-eruption of a non-ankylosed
tooth due to a disturbance in the eruption mechanism (Stellzig-Eisenhauer et al. 2010). PFE is a
rather rare disease with a prevalence of 0.06% (Hanisch et al. 2018) and it can affect both
primary and permanent teeth, but only posterior teeth are affected (Hanisch et al. 2018; Stellzig-
Eisenhauer et al. 2010). Teeth posterior to the most anterior affected tooth are usually affected as
well and the condition is usually asymmetrical (Hanisch et al. 2018; Stellzig-Eisenhauer et al.
2010). PFE can be classified into 3 subtypes (Frazier-Bowers et al. 2007; Stellzig-Eisenhauer et
al. 2010); in type I all affected teeth have a similar lack of eruption potential. In type II a tooth
distal to the most mesial affected tooth has a greater, but still inadequate eruption potential. In
type III patients both forms appear in the various quadrants.
2.2 Clinical impact, health concerns and treatment
The clinical impact of PFE is often very severe. Affected teeth often present dilacerations
resulting in a severe lateral open bite (Stellzig-Eisenhauer et al. 2010) that results in, for
example, eating dysfunction with chewing difficulties.
Treatment options for affected teeth are quite limited (Frazier-Bowers et al. 2007; Hanisch et al.
2018; Stellzig-Eisenhauer et al. 2010), for example extrusion never succeeds because the teeth
become ankylosed as soon as orthodontic force is applied. In very mild cases the teeth can be
treated conservatively by restoring them with onlays and crowns. Otherwise treatment options
are limited to extraction or surgical removal of the affected teeth followed by implantation or
installation of a removable prothesis, the latter often being the only reasonable solution.
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2.3 Inheritance
It has previously been shown that non-syndromic PFE has an autosomal-dominant mode of
inheritance with complete penetrance and variable expressivity (Frazier-Bowers et al. 2007;
Stellzig-Eisenhauer et al. 2010).
2.4 Molecular genetic analysis
In order to identify the genetic cause of PFE parametric linkage analysis with a dominant model
has been performed (Stellzig-Eisenhauer et al. 2010). This analysis identified two regions with a
maximum LOD score of 2.41. Usually an LOD score > 3 is considered an indicator for linkage,
however, this was not achievable due to the given family structure in their cohort. The first
identified region was excluded since no disease-associated mutations were found following
sequencing of exons from two patients and an unaffected control person.
The second identified region was located on chromosome 3 in interval p14.3-p24.3. This section
of the chromosome contains 301 genes. In order to narrow down the number of potential
candidate genes factors such as expression in the bone or bone-associated tissue, functional
considerations on the encoding protein and a known role in disease processes were considered.
This analysis identified the gene encoding parathyroid hormone receptor 1 (PTHR1) as a
potential candidate for the gene responsible for PFE. Additionally, it is known that PTHR1 binds
parathyroid hormone (PTH) and parathyroid hormone-like hormone (PTHLH) with equal
affinity. PTHLH expression is restricted to the epithelial layer during tooth development, while
PTHR1 expression is observed in the adjacent dental mesenchyme and alveolar bone. This
would indicate a role for PTHLH and/or PTHR1 in the signal transduction pathways regulating
epithelial-mesenchymal interactions during the development of epithelial organs such as teeth.
Validation of this hypothesis was undertaken by analysing all 14 PTHR1-coding exons and their
respective intron-exon boundaries using direct sequencing (Stellzig-Eisenhauer et al. 2010). In
each of their four multiplex pedigrees (Families grouped into ZD1, ZD2, ZD3 and ZD11) they
identified one of three distinct heterozygous mutations (ZD1 and ZD3: c.1050-3C>G; ZD2:
c.543+1G>A; ZD11: c.463G>T). These mutations were only observed in study participants that
were affected by PFE (Stellzig-Eisenhauer et al. 2010).
It would therefore seem likely that the autosomal dominant PTHR1 mutation observed in
families with non-syndromic PFE most likely led to premature proteolytic degradation of the
20
precursor protein and that this strongly suggested that haplo-insufficiency of the receptor was the
cause of non-syndromic PFE (Stellzig-Eisenhauer et al. 2010).
2.5 Conclusion
PFE has been shown to have an autosomal dominant mode of inheritance and mutations in the
PTHR1 gene are associated with non-syndromic PFE.
21
3. Materials and methods
3.1 Segregation analysis
3.1.1 Data collection for segregation analysis
• Complete selection
There are many ways of collecting data for segregation analysis. However one such method is to
choose a random sample within the population or through parents with no regard to the
phenotype of the children (Mi 1967). This way of sampling is defined as complete selection and
may include all possible mating types (affected x affected, affected x normal, normal x affected
and normal x normal) and all types of s,r combinations (childless, nonsegregating and
segregating families) s being sibship size and r being number of affected siblings.
• Incomplete selection
In contrast to complete selection incomplete selection includes sampling through the affected
children (Mi 1967). In this way only simplex and multiplex families will be included in the
sample and this will introduce a bias that can result in the proportion of affected individuals
being over estimated. For example, when dealing with a recessive disease it could be possible for
litters from two carriers to not include any affected offspring. These offspring should still be
included in the statistical calculations, but when using incomplete selection, they are not.
3.1.2 Singles method
When data is obtained through incomplete selection as described above a correction for the bias
that this mode of data collection presents is required. This correction can be performed using
Singles method (Nicholas 2003), the object of which is to test if the observed disease frequency
(p) variates from the expected frequency (p0) by a given form of inheritance. We can test if p =
p0 by calculating the test value Z2. If the test value is greater than the critical value of the chi-
square distribution, we reject the null hypothesis (NIST/SEMATECH 2010). When using the
significance level α = 0.05 and 1 degree of freedom the critical value of the chi-square
distribution is 3.841 (NIST/SEMATECH 2010).
The test value Z2 can be calculated as follows (Nicholas 2003):
Z2 = (𝑝^−𝑝0)2
𝐸𝑠𝑡.𝑣𝑎𝑟(𝑝^)
22
Where p^ is an estimate of the true p and can be calculated using the following formula:
𝑝^ = 𝐴−𝐴1
𝑇−𝐴1
And the variance-estimate of p^ can be calculated as follows:
Est.var(p^) = (𝑇−𝐴)
(𝑇−𝐴1)3 {𝐴 − 𝐴1 + 2𝐴2
(𝑇−𝐴)
(𝑇−𝐴1)}
A: Total number of affected offspring
A1: Number of litters with only 1 affected offspring
A2: Number of litters with 2 affected offspring
T: Total number of offspring
3.2 My data
The data used in this study included 35 dogs, 13 males and 22 females, known to have “lanced”
canines and 25 dogs described as being free of “lanced” canines. All the unaffected dogs
included in this study had at least one affected sibling. The full status of offspring in a whole
litter were known for 11 litters.
3.2.1 Data collection and potential issues
• Collecting of data
The initial data, the 35 dogs with “lanced” canines, were collected in different ways. Some
through the Danish Shetland Sheepdog Club as a response to posts regarding the disease, some
through my master’s thesis advisor and some directly to me. The ones directly to me were
through FB posts by the Danish Shetland Sheepdog Club, e-mail correspondence with breeders,
personal meeting with a breeder and through personal friends.
The status of most of the dogs were confirmed through either photographs or the dog visiting a
veterinary professional prior to this study. However, in the case of 3 of the dogs I only have the
owner/breeder’s assessment of the dog being affected.
The status of the 25 unaffected siblings included in this study where collected by incomplete
selection through affected siblings. The data was obtained through e-mail correspondence with
breeders, personal meeting with a breeder and a questionnaire sent out to owners of dogs from
the same litter as an affected dog. The questionnaire included a description of “lanced” canines
and photos (see appendix A).
23
• Potential issues
Overall there are two potential issues with this method of data collection. The first is that the
status of some of the dogs included in this study, mainly within the group described as being
unaffected, is an assessment from the owner or breeder themselves. Thus, even though “lanced”
canines is a fairly simple condition to asses, some dogs who only exhibit mild symptoms of
“lanced” canines might accidently be classified as free of “lanced” canines since the owner or
breeder was not trained in assessing the dogs teeth. Also, the fact that some breeders and dog
owners still believe that wrongly positioned canines is always a result of retained deciduous teeth
could classify an affected dog as free of “lanced” canines. This could result in some dogs being
placed in the wrong category (affected / not affected). If this is the case the overall prevalence of
the condition in this dataset could be underestimated.
Another issue, regarding the segregation analysis, is that incomplete selection was used. As
described earlier this introduces a bias that can result in the proportion of affected individuals
being over estimated.
24
4. Results
4.1 Overview
Looking at the initial data (appendix B) it can be seen that although some dogs do have common
ancestors, this is mainly the case when there are dogs directly related to each other for example
from the same breeder, siblings or mother and offspring. Some have a few common ancestors
although they are not directly related through the same parents, but there is no dog that connects
all of the data (or even just a significant portion of it). The maximum number of dogs sharing a
common ancestor (MD2) is 8 dogs, and 3 of the affected dogs have no connection to any of the
other dogs, at least not in the 4 generations included in this study.
4.2 Singles method
The composition of the 11 litters included in this study can be found in Appendix C with litter A
illustrated below as an example.
25
In summary the dataset was composed of the following litters:
Number of litters with 1 affected offspring 7
Number of litters with 2 affected offspring 3
From this the test value Z2 could be calculated as follows:
𝑝^ = 𝐴−𝐴1
𝑇−𝐴1 =
16−7
41−7 = 0.265
Est.var(p^) = (𝑇−𝐴)
(𝑇−𝐴1)3 {𝐴 − 𝐴1 + 2𝐴2
(𝑇−𝐴)
(𝑇−𝐴1)} =
(41−16)
(41−7)3 {(16 − 7) + (2 ∙
3)((41−16)
(41−7))} = 0.008531
Z2 = (𝑝^−𝑝0)2
𝐸𝑠𝑡.𝑣𝑎𝑟(𝑝^) =
(0.265−0,25)2
0.008531 = 0.0264
As the critical value of chi-square distribution with 1 degree of freedom and a significance level
of 5% is 3.84 the calculated Z2 value shows that there is no significant difference between the
observed segregation frequency and the expected segregation frequency (0.25). Therefore, we
cannot reject the null hypothesis about simple recessive inheritance.
Litter Number of affected
offspring
Littersize
A 3 5
B 2 5
C 2 5
D 1 5
E 2 3
F 1 3
G 1 5
H 1 4
I 1 4
J 1 1
K 1 1
Total 16 41
26
5. Discussion
5.1 Heredity and “lanced” canines
The result from applying Singles method indicates that a simple recessive mode of inheritance
cannot be ruled out. But considering the lack of shared ancestors between the dogs in this study,
and the fact that some dogs have no hereditary link to the other dogs in this study, a simple
recessive mode of inheritance seems unlikely. Although what is clear from the analysis of this
dataset using Singles method is that lanced canines is a condition with a high heritability. This,
together with the fact that the condition has highly variable expressivity and possibly variable
penetrance, would suggest that “lanced” canines is likely a threshold trait where several genes
influence the development of the condition.
5.2 Breeding restrictions and recommendations in the
shetland sheepdog
The Danish Kennel Club (DKK) has a set of breeding restrictions that must be met in order to
have the puppies registered in DKK. There is also a set of breeding recommendations that the
breeders can decide for themselves if they want to follow. But the type of pedigree the puppy
will receive depends on whether the breeder follows only the restrictions (basic pedigree) or both
the restrictions and recommendations (Basic plus pedigree). It is decided by the Danish Shetland
Sheepdog Club what these restrictions and recommendations are.
5.2.1 Restrictions
• Collie eye anomaly (CEA)
For Shetland sheepdogs the restriction states: “Puppies cannot be registered in DKK, unless both
parents, before mating, have been examined for CEA by a member of the Danish Veterinary
Association eye panel or by another veterinary ophthalmologist approved by the DKK. The
optimal time for examination is in the pups 7.-9. weeks of life. The CEA attest applies for life”
(Dansk Kennel Klub)
27
• Colour breeding
Here the restrictions state: “Two Shetland sheepdogs of the colour blue merle are not allowed to
be mated. A Shetland sheepdog of the colour blue merle is not allowed to be mated with a zobel”
(Dansk Kennel Klub)
5.2.2 Recommendations
• Progressive Retinal Atrophy (PRA)
Here the recommendations states: “Before mating both parents must have an eye examination by
a member of the Danish Veterinary Association eye panel or by another veterinary
ophthalmologist approved by the DKK and found free of any signs of PRA. The earliest
examination time is when the dog is 12 months old. Parent animals desired to be used in
breeding after the age of 5 years, must have a new eye examination.” (Dansk Kennel Klub)
• Collie eye anomaly (CEA)
Here the recommendation states: “At least one of the parent animals has to be registered as free
of CEA in DKK by examination before mating. If there, in addition to the eye examination result,
is also a registered DNA status on the dog this must also indicate that the dog is CEA free.”
(Dansk Kennel Klub)
• Show results
Here the recommendation states: “Both parents must be rewarded with at least ‘Very Good’ at
an FCI/DKK acknowledged show before mating” (Dansk Kennel Klub)
5.3 “Lanced” canines and breeding
Our results indicate that “lanced” canines is a condition with high heritability and it should
therefore be recommended to avoid using any affected individuals in breeding. In principle using
any dog for breeding that has previously produced offspring with “lanced” canines, or has
affected siblings, should be avoided, regardless of whether the dog is free from “lanced” canines
itself. Luckily “lanced” canines can be diagnosed clinically before the dog reaches breeding age,
so it is possible to know the disease status before mating. But since “lanced” canines seems to be
widespread in the population, excluding a high number of dogs from the breeding pool could
lead to other effects of inbreeding depression (Lyons 2010). There are also other diseases that
need to be considered when choosing breeding dogs. For example, as described earlier in the
28
breeding restrictions and recommendations for the Shetland sheepdog, the eye diseases CEA and
PRA. With breeding it will always be a compromise between desired traits and undesired traits.
It could therefore be argued that given that “lanced” canines is neither a fatal nor disabling
disease once it is treated it should not be as big a factor in choosing breeding material compared
to more serious diseases. Nevertheless, “lanced” canines can be a big problem for the
individually affected dogs and an economic burden for the owners of these dogs. So breeders
should strive towards reducing the number of affected individuals and eventually, slowly
eradicating the disease altogether.
5.4 Genetic testing
5.4.1 Genetic testing in general
Genetic testing in dogs is of growing importance in veterinary medicine. More and more
mutations that have an impact on canine health or appearance are being discovered, and genetic
tests for these mutations developed. Genetic testing gives veterinarians an important tool for the
diagnosis of diseases. Some non-genetic components, for example toxins and infections, and
some environmental influences, such as diet and exercise, can produce a phenotype that looks
just like an inherited characteristic or disease. In these cases, genetic testing can assist the
veterinarians in finding out more about the underlying cause of the disease. Genetic testing can
also help breeders in choosing their breeding materials and which combinations of dogs to breed,
in order to prevent or even eradicate diseases (Lyons 2010)
5.4.2 Why is finding a possible genetic test a good idea?
Even though “lanced” canines do indeed become evident before the dog reaches breeding age,
and therefore there is no risk of breeding with a dog that will later turn out to be affected, it does
present complications that the disease itself is not clinically evident in puppies before weaning.
This means that puppies can be bought as future breeders and when the permanent canines erupt
and “lanced” canines becomes evident the breeder now has a dog they cannot use as intended.
Given that many of the smaller kennels do not simply have the option to buy a new dog, there is
both a personal and economic cost. On a personal level it might mean that breeders will have to
rehouse the intended breeding dog, since it can no longer be used in breeding, and they might not
have enough space nor the time for both a new dog and the dog with “lanced” canines.
Economically there is of course the direct cost to having the “lanced” canines treated, but there is
also the more hidden cost of lost time with regard to when the kennel can expect puppies, the
29
expenses already used on the dog that is now unfit to breed with, such as food, veterinary bills,
training costs etc and the expense of buying in a new dog for the kennel’s breeding programme.
Thus if a genetic test could be found, then puppies could be tested before weaning and only
puppies free of the condition would be sold as future breeders.
30
6. Conclusion
6.1 My study
“Lanced” canines seems to be a widespread condition amongst Shetland sheepdogs. It has a high
heritability and the development is most likely caused by mutations in several genes. The data
presented in this study points towards it being a threshold trait with both variable penetrance and
variable expressivity. However more studies are needed to try and find the genes responsible for
the condition and make genetic testing possible.
6.2 Breeding recommendations regarding “lanced” canines
It is recommended to avoid the use of any affected individuals in breeding. Furthermore, it is
recommended to never repeat a mating that has previously produced offspring with “lanced”
canines regardless of whether the parent animals are free of “lanced” canines.
31
7. Perspectives
It would be interesting to find the prevalence for “lanced” canines in the Danish Shetland
sheepdog population, this could be done by using the following equation:
𝑃𝑟𝑒𝑣𝑎𝑙𝑒𝑛𝑐𝑒 = 𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑑𝑜𝑔𝑠 𝑖𝑛 𝑡ℎ𝑒 𝑠𝑎𝑚𝑝𝑙𝑒 𝑤𝑖𝑡ℎ 𝑙𝑎𝑛𝑐𝑒𝑑 𝑐𝑎𝑛𝑖𝑛𝑒𝑠
𝑇𝑜𝑡𝑎𝑙 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑑𝑜𝑔𝑠 𝑖𝑛 𝑡ℎ𝑒 𝑠𝑎𝑚𝑝𝑙𝑒
The question would then be how many dogs would we need to sample in such a study? Given
that the objective in a study designed to estimate the prevalence of a given condition in a
geographic area is to sample sufficient population in order to get adequate number of subjects
correctly classified as having the condition of interest or not (Arya, Antonisamy, and Kumar
2012). It would therefore require a large number of randomly selected Shetland sheepdogs to
participate, something that might prove a bit difficult.
It would also be very interesting to get an estimate of the heritability to get an idea about how
much of the variation in “lanced” canines in the population is due to genetic variation. In other
words, to find out how big a role the genetic differences in the population play compared to
environment and random chance. The heritability is expressed as 𝐻2 = 𝑉𝑔
𝑉𝑝
H2 being the heritability estimate, Vg the variation in genotype and Vp the variation in phenotype.
(Meaney and Taylor 2018; Wray and Visscher 2008)
The way you calculate heritability is in short, that you compare how often a disease/condition
occurs in families compared to how often it occurs in the population. So, in order to do this, it is
needed to find the prevalence in the population as discussed above.
Knowing that “lanced” canines is a hereditary disease the next step would be to identify the
gene(s) causing “lanced” canines in order to then develop a genetic test for the condition. This
could for example be done by whole genome sequencing of a dog with “lanced” canines that
could then be compared to a reference dog’s genome to find the sequence variants unique to the
affected dog. Only the sequences that are predicted to result in an altered gene product are of
interest. To narrow it down further one could see if any of the mutated genes would also likely
alter the function of the gene product. One could also see if any of the sequences were located in
genes already associated with dental anomalies. If multiple whole genome sequencing results
from dogs with “lanced” canines are available these could also be compared and all mutant
sequences that are shared among dogs with “lanced” canines, but not with reference dogs free of
“lanced” canines, could be of interest for further analysis.
32
References
Arya, Ravindra, Belavendra Antonisamy, and Sushil Kumar. 2012. “Sample Size Estimation in
Prevalence Studies.” Indian Journal of Pediatrics 79(11): 1482–88.
Bartges, Joe et al. 2012. “AAHA Canine Life Stage Guidelines*.” Journal of the American
Animal Hospital Association 48(1): 1–11.
Dansk Kennel Klub. “Dansk Kennel Klub Avl/Sundhesrestriktioner Shetland Sheepdog.”
https://www.hundeweb.dk/dkk/public/openPage/tjenester/avlsrestriksjoner/raseData.html?R
AID=0880 (May 31, 2018).
Frazier-Bowers, Sylvia A, Karen E Koehler, James L Ackerman, and William R Proffit. 2007.
“Primary Failure of Eruption: Further Characterization of a Rare Eruption Disorder.(Author
Abstract).” American Journal of Orthodontics & Dentofacial Orthopedics 131(5):
578.e1-578.e11.
Hanisch, Marcel, Lale Hanisch, Johannes Kleinheinz, and Susanne Jung. 2018. “Primary Failure
of Eruption (PFE): A Systematic Review.” HEAD & FACE MEDICINE 14.
Legendre, Loïc, and Kevin Stepaniuk. 2008. “Correction of Maxillary Canine Tooth
Mesioversion in Dogs.” Journal of Veterinary Dentistry 25(3): 216–21.
Lyons, Leslie A. 2010. “Feline Genetics: Clinical Applications and Genetic Testing.” Topics in
Companion Animal Medicine 25(4): 203–12.
Mackenzie, A, M W Ferguson, and P T Sharpe. 1992. “Expression Patterns of the Homeobox
Gene, Hox-8, in the Mouse Embryo Suggest a Role in Specifying Tooth Initiation and
Shape.” Development (Cambridge, England) 115(2): 403.
Matzuk, Martin M. et al. 1995. “Functional Analysis of Activins during Mammalian
Development.” Nature 374(6520): 354–57.
Meaney, F. John, and Cynthia Taylor. 2018. “Heritability.” Encyclopædia Britannica.
Mi, Ming-Pi. 1967. “Segregation Analysis.” American Journal of Human Genetics 19(3 Pt 1):
313–21.
Nicholas, F W. 2003. Introduction to Veterinary Genetics. 2. ed. ed. F W Nicholas. Oxford:
Blackwell Publishing.
NIST/SEMATECH. 2010. “E-Handbook of Statistical Methods.”
https://www.itl.nist.gov/div898/handbook/eda/section3/eda3674.htm (June 8, 2018).
Pretzer, S D. 2008. “Canine Embryonic and Fetal Development: A Review.” Canine embryonic
and fetal development: A review 70(3): 300–303.
Qiu, M et al. 1997. “Role of the Dlx Homeobox Genes in Proximodistal Patterning of the
33
Branchial Arches: Mutations of Dlx-1, Dlx-2, and Dlx-1 and -2 Alter Morphogenesis of
Proximal Skeletal and Soft Tissue Structures Derived from the First and Second Arches.”
Developmental biology 185(2): 165.
Satokata, Ichiro, and Richard Maas. 1994. “Msx1 Deficient Mice Exhibit Cleft Palate and
Abnormalities of Craniofacial and Tooth Development.” Nature Genetics 6(4): 348.
Sharpe, Paul T. 1995. “Homeobox Genes and Orofacial Development.” Connective Tissue
Research 32(1–4): 17–25.
Stellzig-Eisenhauer, Angelika et al. 2010. “Primary Failure of Eruption (PFE) – Clinical and
Molecular Genetics Analysis.” Official Journal of the German Orthodontic Society /
Offizielle Zeitschrift der Deutschen Gesellschaft für Kieferorthopädie 71(1): 6–16.
Teaford, Mark F, Mark W J Ferguson, and Moya Meredith Smith, eds. 2000. “Genes, Molecules
and Tooth Initiation.” In Development, Function and Evolution of Teeth, Cambridge:
Cambridge University Press, 1–12.
Thomas, B L et al. 1997. “Role of Dlx-1 and Dlx-2 Genes in Patterning of the Murine
Dentition.” Development (Cambridge, England) 124(23): 4811.
Tsugawa, Anson J., Milinda J. Lommer, and Frank J.M. Verstraete. 2012. Oral and Maxillofacial
Surgery in Dogs and Cats Extraction of Canine Teeth in Dogs. Elsevier Ltd.
Tutt, Cedric. 2006. Small Animal Dentistry, a Manual of Techniques. eds. Cedric Tutt and Wiley
InterScience (Online service). Oxford Ames, Iowa : Blackwell Pub.
Vaahtokari, A et al. 1996. “The Enamel Knot as a Signaling Center in the Developing Mouse
Tooth.” Mechanisms of development 54(1): 39.
Williams, R C, and H E Evans. 1978. “Prenatal Dental Development in the Dog, Canis
Familiaris: Chronology of Tooth Germ Formation and Calcification of Deciduous Teeth.”
Anatomia Histologia Embryologia 7(2): 152–63.
Wray, N, and P Visscher. 2008. “Estimating Trait Heritability.” Nature education 1(1): 29.
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Appendix
Appendix A – Dog owner questionnaire
Denne mail er udsendt fra DKK for at hjælpe Dansk Shetland Sheepdog Klub og specialestuderende Lena Rahbek med et forskningsprojekt. Kære hundeejer, På Dansk Shetland Sheepdog Klubs opfordring er der etableret et veterinært specialeprojekt på KU/SUND, som har til formål at undersøge arvegangen for Lansetænder (fejlstillede hjørnetænder i overmunden – se fotos nederst). Der er, på frivillig basis, indsamlet oplysninger om forekomsten af denne tanddefekt i den danske population, og i den forbindelse har det vist sig, at en kuldsøskende til din hund født DD/MM-YYYY har/har haft Lansetænder. For at finde arvegangen skal der så vidt muligt indsamles oplysninger fra hele kuld. Det vil derfor være en stor hjælp for projektet, hvis du vil oplyse din hunds status i forhold til Lansetænder. Oplysningerne vil blive anonymiseret og behandlet fortroligt. Du svarer ved at besvare denne mail og krydse af i nedenstående skema:
Min hund har/har haft ”Lansetænder”
Min hund har ikke/har ikke haft ”Lansetænder”
Ved ikke*
Andet (beskriv f.eks. om hunden har andre tandfejl)
*Hvis du er i tvivl, er du velkommen til at sende billeder af hundens hjørnetænder i begge sider. Så kan vi hjælpe med at vurdere dem.
Hvad er en lansetand?
En lansetand er en tandstillingsfejl hvor hjørnetanden i overmunden peger fremad. Graden kan variere meget. Herunder et par fotos af en lansetand:
Med venlig hilsen/Kind regards, DANSK KENNEL KLUB
35
Appendix B – Initial data overview
Same colour box&text = same dog
Same colour full pedigree = dogs from the same litter
36
Appendix C – Litter compositions litters A till K
37
38
39